This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-359935, filed Dec. 17, 1999; and No. 11-360990, filed Dec. 20, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an apparatus for forming a coating film on a substrate to be treated such as a semiconductor wafer or an LCD substrate (a glass substrate for a liquid crystal display) by applying a coating solution, for example, a resist solution or the like thereto, and a coating unit.
In fabrication processes of a semiconductor device or an LCD, a resist pattern for a substrate to be treated is formed by a technology called photolithography. An apparatus for forming the resist pattern is composed by connecting an aligner to a coating and developing system provided with a cassette mounting section for carrying a wafer into/from a cassette, a coating unit for applying a resist solution, thermal treatment units for performing treatments such as heating and cooling, a developing unit for performing development, a main arm for transferring the wafer and so on.
Conventionally, the resist solution has been applied in the above-described coating unit by a so-called spin coating method. This is a method by which the resist solution is spread by centrifugal force of the wafer so that a solution film is formed over the entire wafer by providing a rotatable spin chuck in a cup surrounding the sides of the substrate over the entire circumference thereof, horizontally suction-holding the wafer by the spin chuck, and rotating the wafer while supplying the resist solution to the wafer from a nozzle above the central portion of the wafer.
Incidentally, a line width of the resist pattern to be formed is proportional to a film thickness of a resist film and an exposure wavelength. Accordingly, formation of thinner films is attempted by increasing the rotational frequency of the wafer in the spin coating method since it is necessary to make a solution film thinner to a minimum in order to cope with growing demands for a finer pattern in recent years.
However, since the wafer is rotated at a high speed in the above-described method, there is a problem that a circumferential speed of the inner circumferential portion of the wafer becomes high compared with that of the outer circumferential portion thereof, whereby air turbulence occurs at the outer peripheral portion of the wafer particularly when the wafer is upsized. The turbulence becomes a factor of impairing the formation of finer patterns since it changes the film thickness, bringing about the non-uniformity in film thickness of the entire wafer.
Further, the resist solution is spread to be blown off from the central portion of the wafer toward the peripheral portion thereof, causing a big waste of resist solution since it scatters from the peripheral portion thereof to the side of the cup. In addition, there has been a problem that the resist solution applied to portions except for a circuit formation region such as the peripheral portion or the resist solution adhered to the cup due to the scatter is hardened, which results in a cause of particles.
In view of such circumstances, a method independent of the spin coating method has been examined. According to this method, a resist solution is supplied to a wafer W in a manner of so-called single stroke by reciprocating a nozzle N in an X-direction and at the same time intermittently moving the wafer W in a Y-direction while supplying the resist solution RE from a discharge hole having a fine diameter of the nozzle N provided above the wafer W as shown in FIG. 34. Incidentally, it is preferable that the portions except for the circuit formation region on the wafer W are covered with a mask to prevent the resist solution from adhering to the periphery or the back surface of the wafer W in this case.
The wafer W is not rotated in this method, whereby the inconvenience as described above is resolved and application can be performed without causing waste. However, a thinner which dissolves a resist constituent is not shaken off unlike in the spin coating and remains intact on the wafer. For example, although no more than about 10% of the thinner remains when the spin coating is performed, substantially 100% of the thinner remains in the manner of single stroke. Therefore, when the wafer is transferred to a heating plate and undergoes drying after being applied with the resist solution, it requires long time to volatilize the thinner, and an amount of volatilization varies within the wafer since it is hard to evenly conduct heat to the resist solution, whereby the uniformity in film thickness of the film to be obtained is deteriorated even if the resist solution is uniformly applied purposely. Further, variations in the amount of volatilization within wafer become wide while the wafer is transferred to the heating plate by a main arm since the amount of volatilization is large on the wafer after being applied with the resist solution, also resulting in a factor which deteriorates the uniformity in film thickness of the resist film.
The present invention is made in view of the aforesaid circumstances and its object is to provide a coating film forming apparatus capable of increasing yields of a coating solution and forming a uniform coating film, and a coating unit.
A coating film forming apparatus according to the present invention comprises a cassette mounting section on which a substrate cassette housing a plurality of substrates is mounted, a coating unit for applying the coating solution to the substrate taken out of the substrate cassette which is mounted on the cassette mounting section, plural treatment units for performing at least either pre-treatment or post-treatment for treatment of applying the coating solution, and a main transfer mechanism for transferring the substrate between the coating unit and the treatment units, the coating unit having (a) a coating section including a substrate holding portion for holding the substrate, a coating solution nozzle for discharging the coating solution to the substrate, provided to be opposed to the substrate held by the substrate holding portion, and a drive mechanism for moving the coating solution nozzle relatively to the substrate along a surface thereof while discharging the coating solution to the surface of the substrate from the coating solution nozzle, and (b) a reduced-pressure drying section for drying under a reduced-pressure atmosphere the substrate which is applied with the coating solution in the coating section. In this invention, application is performed while the coating solution is discharged, for example, in a line shape having a fine diameter from the coating solution nozzle. In addition it is preferable to employ a mask for covering portions except for a region of coating film formation on the substrate and receiving the coating solution from the coating solution nozzle.
According to this invention, quick drying can be performed since drying is performed under reduced pressure even if a large amount of solvent remains in the coating solution applied to the substrate, and a temperature of the coating film within wafer can be maintained uniform by non-heating or heating at a low temperature even if heating is performed. Additionally, drying under reduced pressure can be quickly performed before volatilization of the solvent proceeds so far without waiting the main transfer mechanism after the application since the reduced-pressure drying section is provided in the coating unit, whereby the uniformity within the substrate in film thickness of the coating film can be maintained. Hence, it is possible to increase the yields of the coating solution and besides form the uniform coating film.
The coating unit may be structured to so as to be provided with a coating film removing section for removing the coating film at a peripheral portion of the substrate which is dried under reduced pressure in the reduced-pressure drying section, and in this case it may be structured so as to be provided with an auxiliary transfer mechanism for transferring the substrate between the substrate holding portion, the reduced-pressure drying section, and the coating film removing section. Further, the reduced-pressure drying section may be structured so as to have a mounting portion for placing the substrate thereon, a closed container for making an atmosphere in which the substrate is placed on the mounting portion a closed atmosphere, and pressure reducing means for reducing pressure inside the closed container, and in this case it may be structured that the closed container is divided into an upper side portion and a lower side portion, and the upper side portion and the lower side portion are provided to detachably join with each other. The mounting portion in the reduced-pressure drying section may be used also as the substrate holding portion in the coating section.
To be more specific, the coating film removing section may be structured to be provided with a substrate holding portion for holding the substrate, a surrounding member having a C-shape cross section so as to sandwich the peripheral portion of the substrate held by the substrate holding portion, a solvent nozzle provided to be opposed to the surface of the substrate in the surrounding member, and suction means for sucking an atmosphere surrounded by the surrounding member. Further a detecting portion for optically detecting the peripheral portion of the substrate held by the substrate holding portion in the coating film removing section may be provided and the substrate holding portion may be rotated so that the substrate is oriented in a predetermined direction based on a result of a detection by the detecting portion. Furthermore, reception and delivery of the substrate from/to the main transfer mechanism in the coating unit may be performed via substrate holding portion in the coating film removing section.
Moreover, the present invention may be structured as follows. Namely, it comprises a cassette mounting section on which a substrate cassette housing a plurality of substrates is mounted, a coating unit for applying the coating solution to the substrate taken out of the substrate cassette which is mounted on the cassette mounting section, plural treatment units for performing at least either pre-treatment or post-treatment for treatment of applying the coating solution, a reduced-pressure drying unit for drying under a reduced-pressure atmosphere the substrate which is applied with the coating solution in the coating unit, provided as one of the plural treatment units, and a main transfer mechanism for transferring the substrate between the coating unit and the treatment units, the coating unit having a substrate holding portion for holding the substrate, a coating solution nozzle for discharging the coating solution to the substrate, provided to be opposed to the substrate held by the substrate holding portion, and a drive mechanism for moving the coating solution nozzle relatively to the substrate along a surface thereof while discharging the coating solution to the surface of the substrate from the coating solution nozzle, the main transfer mechanism having a holding member for holding the substrate and atmosphere forming means for making an atmosphere in which the substrate is held by the holding member an atmosphere in which vaporization of solvent is inhibited. In this invention, a coating film removing unit for removing the coating film at the peripheral portion of the substrate which is dried under reduced pressure in the reduced-pressure drying unit may be provided as one of the treatment units. The atmosphere forming means has, for example, a cover body for surrounding a circumference of the substrate held by the holding member and, for example, means for supplying solvent vapor. Alternatively, the atmosphere forming means may be means for making the atmosphere at least either an atmosphere at a predetermined temperature or an atmosphere at a predetermined humidity. Only the cover body may be provided.
According to such invention, the volatilization of the solvent from the coating solution can be inhibited when the substrate after being applied is transferred by the main transfer mechanism, whereby it is possible to maintain the uniformity within the substrate in film thickness of the coating film. In this case, it is preferable that the main transfer mechanism has washing means for washing the holding member, for example, means for supplying a washing solution to the holding member and means for supplying gas for drying to the holding member. Further it is desirable that the main transfer mechanism has detecting means for detecting a stain of the holding member, since it is possible to determine the timing when the holding member is to be washed.
Additionally, in the present invention, a coating unit for forming a coating film on a substrate by supplying a coating solution to the substrate from coating solution discharge means comprises a container for housing the substrate therein, solvent-atmosphere generating means for supplying solvent vapor of the coating solution to the inside of the container to generate a solvent atmosphere at a predetermined concentration inside the container, intake means for sucking the atmosphere inside the container, a sensor for detecting a concentration of the solvent atmosphere inside the container, and control means for controlling operation of the solvent-atmosphere generating means and operation of the intake means based on the concentration detected by the sensor.
According to the coating unit, the concentration of the solvent atmosphere inside the container is detected by the sensor and a result of the detection by the sensor is inputted to the control means. Here, the control means operates the solvent-atmosphere generating means to generate the solvent atmosphere at the predetermined concentration inside the container when the concentration of the solvent atmosphere inside the container is lower than the predetermined concentration. On the other hand, when the concentration of the solvent atmosphere inside the container is higher than the predetermined concentration, the control means operates the intake means so that the solvent atmosphere inside the container is sucked. Accordingly, the concentration of the solvent atmosphere inside the container can be maintained constant since it is possible to rapidly cope with the concentration change of the solvent atmosphere.
According to the coating unit, it is possible to increase the yields of the coating solution and besides form the uniform coating film. In addition, it is possible to rapidly cope with the concentration change of the solvent atmosphere inside the container, thereby enabling the concentration of the solvent atmosphere to be maintained constant. As a result, formation of the film which is a thin film and uniform in film thickness can be realized and, for example, fabrication of a semiconductor device of high quality or the like is made possible. Further, a throughput can be improved. Moreover, it is possible to rapidly generate the solvent atmosphere at the predetermined concentration inside the container by supplying the solvent vapor and maintain the solvent atmosphere inside the container at the predetermined concentration by performing intake.
In the coating unit, the solvent-atmosphere generating means has a tank for storing the solvent therein and a heating mechanism for heating the solvent in the tank, and it is preferable that heating by the heating mechanism is controlled by the control means. According to such structure, the control means accelerates heating by the heating mechanism so that an amount supplied of the solvent vapor can be increased when the concentration of the solvent atmosphere inside the container is lower than the predetermined concentration. Therefore, it is possible to rapidly make the concentration of the solvent atmosphere inside the container the predetermined concentration.
In addition, it is preferable that the coating unit comprises a cover for opening and closing a carrier inlet/outlet of the container, the cover being formed with a slit through which the coating solution supply means is movable, an intake port being arranged in the vicinity of the slit. According to such structure, the atmosphere inside the container can be sucked through the intake port arranged in the vicinity of the slit. Moreover, the intake means may have an intake port formed on the container so that intake may be performed also through this intake port.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.